VANOS Control

With the introduction of double VANOS, the valve timing is changed on both the intake and the exhaust camshafts.

Double VANOS provides the following benefits:

• Torque increase in the low to mid (1500 - 2000 RPM) range without power loss in the upper RPM range.
• Less incomplete combustion when idling due to less camshaft overlap (also improves idle speed characteristics).
• Internal exhaust gas recirculation (EGR) in the part load range (reduces NOx and post-combustion of residual gasses in the exhaust)
• Rapid catalyst warm up and lower "raw" emissions after cold start.
• Reduction in fuel consumption

Double VANOS consists of the following parts:

• Intake and exhaust camshafts with helical gear insert
• Sprockets with adjustable gears
• VANOS actuators for each camshaft
• 2 three-way solenoid switching valves
• 2 impulse wheels for detecting camshaft position
• 2 camshaft position sensors (Hall effect)

The "initial" timing is set by gear positioning (refer to the appropriate REPAIR INSTRUCTIONS article for details) and the chain tensioner. As with the previous VANOS, the hydraulically controlled actuators move the helical geared cups to regulate camshaft timing. The angled teeth of the helical gears cause the pushing movement of the helical cup to be converted into a rotational movement. This rotational movement is added to the turning of the camshafts and cause the camshafts to "advance" or "retard". The adjustment rate is dependent oil temperature, oil pressure, and engine RPM.

When the engine is started, the camshafts are in the "fail-safe" position (deactivated). The intake camshaft is in the RETARDED position - held by oil pressure from the sprung open solenoid. The exhaust camshaft is in the ADVANCED position - held by a preload spring in the actuator and oil pressure from the sprung open solenoid.

After 50 RPM (2-5 seconds) from engine start, the ECM is monitoring the exact camshaft position.

The ECM positions the camshafts based on engine RPM and the throttle position signal. From that point the camshaft timing will be varied based on intake air and coolant temperatures.

The double VANOS system is "fully variable". When the ECM detects the camshafts are in the optimum positions, the solenoids are modulated (approximately 100-220 Hz) maintaining oil pressure on both sides of the actuators to hold the camshaft timing.